The hormones released from the neuroendocrine bag cells of Aplysia induce egglaying and the associated behavior. This simple system provides a model in which to study peptide hromones that act at both the organ level and the neuronal level. We propose to isolate the hormones released by these cells, to determine the primary structure of these peptides by HPLC and mass spectrometry, and to determine which are active on the ovotestis and which may have neuronal activity. Isolation and structural characterization is a prerequisite to detailed studies of the mechanism of action of these hormones. We have isolated the peptides from the bag cells of 900 Aplysia brasiliana and have fractionated this material on calibrated Sephadex columns. This study has revelaed major peptides of 22,000, 12,600 and 10,400 MW. Three smaller peptides of 8,100, 3,000 and 2,330 MW were also found and these are now being purified by HPLC. We have made several improvements in the determinization of the structure of peptides by mass spectrometry which will be utilized in this study.